1. Field of the Invention
The invention relates to a bicycle drive chain, more particularly to an improved outer chain plate of a bicycle drive chain.
2. Description of the Related Art
The construction of a conventional bicycle drive chain has been modified continuously in order to achieve smoother operation of the bicycle transmission system and in order to facilitate shifting of the gear ratio. Ease of shifting of the gear ratio depends primarily on the construction of the outer chain plate of the bicycle drive chain. There are two important factors usually considered in the design of the outer chain plate. First, the outer chain plate should be designed so as to minimize friction between the outer chain plate and the sprocket wheels, thereby reducing the noise that is generated when the bicycle transmission system is in motion or when the gear ratio is being shifted. Second, the outer chain plate should be designed so as to facilitate engagement between the bicycle drive chain and the teeth of a selected sprocket wheel when the gear ratio is shifted.
The following are several examples of bicycle drive chain patents which have been granted in the United States:
U.S. Pat. Nos. 5,098,349 and 5,066,265 disclose a chain which includes inner and outer chain plates that have inclined surfaces along upper and lower edges of an inner face thereof. The inclined surfaces cooperatively form curved surfaces to facilitate sliding of a tooth of a sprocket into a space defined by either the inner or outer chain plates of the chain. U.S. Pat. No. 5,151,066 discloses a streamline chain which includes inner and outer chain plates that have inclined surfaces along upper and lower edges of an inner face thereof. As with the two previous patents, the inclined surfaces facilitate sliding of a tooth of a sprocket into a space defined by either the inner or outer chain plates of the streamline chain.
Note that the above three patents are directed to a bicycle drive chain which is capable of engaging smoothly the teeth of a selected sprocket wheel when the gear ratio is shifted.
In order to minimize friction between the outer chain plate and the sprocket wheels, U.S. Pat. No. 4,978,327 discloses a chain which includes an outer chain plate that is formed with a recess to receive one end of a pin therein, thereby preventing the pin from projecting relative to the outer surface of the outer chain plate so as to minimize the generation of friction. The same technique is applied in U.S. Pat. No. 4,983,147 to reduce the noise that is generated when the bicycle transmission system is in motion or when the gear ratio is being shifted.
Note that each of the above described conventional bicycle drive chains can satisfy only one of the aforementioned factors. Furthermore, both the inner and outer plates of the conventional bicycle drive chain are modified in order to satisfy said one of the aforementioned factors.